1. Field of the Invention
The invention relates to an inner-focusing type telephoto lens system used in a digital still camera or a digital video camera.
2. Description of the Related Art
Recently, digital cameras or video cameras having a solid-state imaging device, such as charge-coupled devices (CCDs) and complementary metal-oxide semiconductors (CMOS), are becoming very popular.
In a video camera or a digital camera, bright telephoto lenses with small F numbers are preferred. However, such bright lenses are relatively large and heavy, and thus auto-focusing cameras experience slow focusing with such lenses.
Although various focusing mechanisms have been suggested to resolve the slow focusing, none of them may provide both sufficient brightness and sufficient weight reduction at the same time. For example, a bright telephoto lens with an F number of 1.4 includes a focus lens group having 5 lenses. However, due to such a large number of lenses, the telephoto lens provides insufficient weight reduction. On the other hand, a telephoto lens with a relatively reduced weight includes a small number of lenses, for example, one or two lenses, exhibits a relatively high F number, e.g., about 2, and thus the telephoto lens provides insufficient brightness.
Furthermore, due to recently increasing demands for image quality, effects of hand shakes are not negligible, and thus demands for hand shake correction are increasing. However, lenses in F1.4 class do not have a hand shake correction feature.